Ectopic Parathyroid Adenoma as a Secondary Cause of Severe Resistant Hypercalcemia

Introduction:

Background: Resistant hypercalcemia is defined as persistently elevated calcium levels despite multiple therapy modalities. The most common etiologies include primary hyperparathyroidism (PHPT) and malignancy (1). The parathyroid glands are generally located adjacent to the thyroid but are ectopic in an estimated 2% of the population (2). Here we present a case of PHPT caused by an ectopic parathyroid adenoma complicated with resistant hypercalcemia-induced pancreatitis.

Case Description:
Clinical Case: A 59-year-old Hispanic female presented severe pain beneath her right rib radiating to the back with associated nausea and vomiting. No history of trauma or alcohol abuse. Initial labs revealed elevated lipase (3420 units/L, n <78 units/L) and elevated serum calcium (16 mg/dL, n <10.7 mg/dL), CT of the abdomen/pelvis revealed pancreatic tail fluid collection and pancreatic necrosis. Clinical presentation was consistent with acute pancreatitis secondary to hypercalcemia. 

Further workup showed elevated PTH (1620.5 pg/mL, n <77.1 pg/mL), elevated ionized calcium (1.69 mmol/L, n <1.32 mmol/L), and parathyroid SPECT imaging revealed an ectopic parathyroid adenoma located in the left upper chest behind the medial end of the left clavicle, at the level of the left brachiocephalic vein. The treatment of hypercalcemia consisted of rehydration therapy, a single dose of IV pamidronate 90 mg, four doses of calcitonin 280 units subcutaneously, and cinacalcet 90 mg BID. However, she remained with a calcium level that ranged from 14.5 mg/dL to 20 mg/dL; eventually, she required intermittent hemodialysis to decrease the calcium level and proceed with surgical excision of the adenoma by thoracoscopy. Histopathology confirmed parathyroid adenoma, 2.5 cm.

The postoperative course was complicated by hypocalcemia (hungry bone syndrome), evidenced by elevated alkaline phosphatase (624 units/L, n <120 units/L) and nadir serum calcium (6.3 mg/dL, n>8.9 mg/dL). Other clinical sequelae during hospitalization included acute respiratory failure, shock, and acute renal failure resulting from acute pancreatitis. Hungry bone syndrome improved on supplementation with calcitriol, cholecalciferol, and calcium carbonate tablets. She was discharged home once she could tolerate oral intake and was clinically stable.

Discussion:

Conclusion: This case describes the clinical course of PHPT caused by an ectopic adenoma, complicated with resistant hypercalcemia. It also highlights various treatment modalities that can be used to treat hypercalcemia.